Comparison of maximal inspiratory pressure, tracheal airway occlusion pressure, and its ratio in the prediction of weaning outcome: impact of the use of a digital vacuometer and the unidirectional valve.

OBJECTIVE

To investigate the predictive value of the maximal inspiratory pressure obtained by a digital vacuometer using a unidirectional valve (P(ImaxUV)) as to weaning outcome, and to compare its performance with the respiratory drive using airway occlusion pressure at 0.1 second (P(0.1)), and P(0.1)/P(ImaxUV).

METHODS

Patients on mechanical ventilation for > 24 hours who fulfilled the weaning criteria were prospectively enrolled. Measurements of P(ImaxUV) and P(0.1) were accomplished with a digital vacuometer with a unidirectional valve that allows only exhalation. Measured values were electronically recorded and stored on the digital vacuometer measurement device. Cutoff points for the used parameters were: absolute values of P(ImaxUV) > 30 cm H(2)O, P(0.1) < 2.3 cm H(2)O, and P(0.1)/P(ImaxUV) < 0.10. Receiver operating characteristic curves were calculated to compare the predictive values of the indexes.

RESULTS

One hundred three subjects completed the test. The areas under the receiver operating characteristic curve were 0.79 ± 0.04, 0.65 ± 0.05, and 0.74 ± 0.04 for P(ImaxUV), P(0.1), and P(0.1)/P(ImaxUV), respectively. The area under the receiver operating characteristic curve for P(ImaxUV) was higher than for P(0.1) and P(0.1)/P(ImaxUV), but statistical significance was only found against P(0.1) (P = .007).

CONCLUSIONS

Every studied index had only a modest performance regarding prediction of weaning outcome. Of note, P(ImaxUV) values obtained by digital technology using a unidirectional valve performed better than historically reported using a conventional techniques, surpassing P(0.1) and P(0.1)/P(ImaxUV) in this regard.